These studes propose a continuing investigation of prolactin, its characterization and measurement in human beings, the methods by which its secretion is controlled, and its physiological role in normal and diseased states, including pituitary tumors and cancer of the breast. The principal means of investigation will be radioimmunoassay, supplemented by bioassay and radioreceptor assay. Also to be studied are other anterior pituitary hormones, particularly growth hormone, as well as the posterior pituitary peptides vasopressin, oxytocin, and the neurophysins.